How to search exact phrase from a file which consist of set of phrase with hyphen

I have the file, which consists of a couple of phrases as follows. I would like to grep the exact match from out of them.

file.txt

abc
abc-def
xyz
xyz-pqr
pqrs

If I search "abc" I need to return only abc.
or
if I search "abc-def" i need to return only "abc-def"

preferd output

$grep -w "abc" file.txt
abc

or

$grep -w "abc-def" file.txt
abc-def

the below method is not working for the hyphens

$grep -w abc file.txt 

>Solution :

With your given data/file you can use the -x flag.

grep -x abc file.txt

grep -x abc-def file.txt

• -x, –line-regexp force PATTERN to match only whole lines

• The -x flag is defined/required by POSIX grep(1)